SUMMARY The proposed study aims to develop models of ATD using patient-derived cells and use these models to confirm previously identified modifiers of ATD and test potential drug therapies for ATD in human cells. We have shown that stem cell-derived hepatocyte-like cells (iHeps) generated by differentiating stem cells from patients with liver vs. lung manifestations of ATD exhibit differences in ultrastructural morphology and kinetics of mutant ATZ disposal. Based on these findings, we hypothesize that genetic variations other than the ATZ mutation determine the clinical phenotype of ATD. As a part of the previous cycle of this program project, we and our colleagues have used high throughput analysis in C. elegans using a siRNA library to identify several genes that modify ATZ accumulation. The proposed project will reveal the differences in accumulation of ATZ and its proteotoxicity in iHeps from various subsets of ATD patients delinieated by age of onset of liver disease, disparate hepatic phenotype, presence of co-existing pulmonary disease or hepatocellular carcinoma, and heterozygosity for the ATZ allele. We will also examine a) the extent to which in vitro characteristics of iHeps correspond to various ATD clinical subsets, b) the role of genetic modulators on ATD liver disease phenotypes, c) the response of iHeps to candidate drugs for the treatment of ATD, and d) whether the delay in ATZ disposal that characterizes iHeps from ATD patients with severe liver disease is due to aggregation-prone properties of ATZ. Finally, we will generate in vivo models of human ATD by repopulating the livers of retrorsine-treated immune deficient rats with primary human hepatocytes and iHeps from ATD patients and controls. The development of in vivo and in vitro models of ATD using patient-derived cells would greatly benefit the discovery and validation of target genes for novel therapies of ATD and evaluation of potential therapeutic drugs.